Methods and apparatus for predicting performance of a measurement method, measurement method and apparatus

Abstract

Target structures such as overlay gratings (Ta and Tb) are formed on a substrate (W) by a lithographic process. The first target is illuminated with a spot of first radiation (456a, Sa) and simultaneously the second target is illuminated with a spot of second radiation (456b, Sb). A sensor (418) detects at different locations, portions (460x−, 460x+) of said first radiation that have been diffracted in a first direction by features of the first target and portions (460y−, 460y+) of said second radiation that have been diffracted in a second direction by features of the second target. Asymmetry in X and Y directions can be detected simultaneously, reducing the time required for overlay measurements in X and Y. The two spots of radiation at soft x-ray wavelength can be generated simply by exciting two locations (710a, 710b) in a higher harmonic generation (HHG) radiation source or inverse Compton scattering source.

Description

FIELD[0001]The present disclosure relates to methods and apparatus for inspection (e.g., metrology) usable, for example, in the manufacture of devices by lithographic techniques and to methods of manufacturing devices using lithographic techniques.BACKGROUND[0002]A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will con...

AI Technical Summary

Benefits of technology

[0014]In this way, measurements of, for example, measurements asymmetry can be made on two targets simultaneously, even without the facility of dark-field imaging. The measurement of two targets simultaneously greatly reduces the measurement overhead required to measure a number of targets in different directions.

Problems solved by technology

This limits the smallest features that can be measured, so that the technique can no longer measure directly the smallest features made in modern lithographic processes.

Unfortunately, the cost and other limitations of optical systems compatible with such wavelengths make it commercially unattractive to implement small-target dark-field imaging.

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